I. Field of the Invention
The present invention relates to automatic gain control circuits. More particularly, the present invention relates to a novel and improved closed loop automatic gain control gain control circuit with linear gain control over a very high dynamic range.
II. Description of the Related Art
Automatic gain control (AGC) circuits are widely used in receivers for controlling the gain applied to a signal to be processed. In both analog and digital signal receivers AGC circuits are implemented using different techniques. In analog receivers analog techniques are commonly used while in digital receivers, digital techniques are applied.
In analog receivers, such as used in narrowband FM cellular telephones, the power of the received signal is merely limited typically by clipping the signal. However, such an analog signal processing technique is not applicable to digital receivers since a clipping of a signal modulated with digital data would result in corruption of the data.
Typically in digital receivers, the level of signal power is detected, digitized and then measured. The measured value is typically compared with a set value and an error value generated, all values being in digital form. The error value is then used to control the gain of an amplifier so as to adjust the signal strength to coincide with the desired signal power.
Digital AGC techniques however are relatively slow in controlling signal power due to saturation of the error signals involved in actually controlling the power. Digital techniques thus have the disadvantage of failing to provide accurate power control in environments where signal strength is rapidly changing, and particularly over a high dynamic range.
It is therefore an object of the present invention to provide a novel and improved AGC circuit for rapid, high dynamic range signal power control.
It is yet another object of the present invention to provide an AGC circuit capable of providing gain control over both wideband and narrowband signals so as to maintain received signal power at a constant level.
It is still a further object of the present invention to provide an AGC circuit capable of providing a control signal which can be used in controlling transmitter power.